The present invention relates generally to disk storage devices (e.g., magnetic disk drives or optical disk drives) that move a head relative to a storage medium, and more specifically to techniques for improving the head positioning.
In a conventional track access control system included in a magnetic disk drive or an optical disk drive, a voice-coil motor (VCM) is used to move one or more read/write heads to and positioning them at a desired track. A controller forms a positioning feedback loop and gives a control input to a drive circuit. The drive circuit includes a current feedback amplifier that feeds back VCM drive current. A head support mechanism that supports the read/write head is accelerated by the VCM, wherein the acceleration is proportional to the control input for a head-positioning control operation (see e.g., Japanese published application JPA 2000-222837).
In other prior art, a disk access control system uses a current feedback amplifier, and obtains the speed of a read/write head by differentiating a head-position signal. In this way, the speed information is monitored, and the speed is reduced to zero in case of a defect. (see e.g., Japanese published application JPA 2001-250345).
Further, in other prior art, in a load-unload type head control system using a current feedback amplifier, a read/write head is positioned by a low-speed control in loading an unloaded read/write head to the disk, as distinguished from a seek operation (see e.g., Japanese published application JPA 2002-93080).
The drive circuit of the positioning control system disclosed in Japanese published application JPA 2000-222837 includes a current feedback amplifier that feeds back a current supplied to a VCM. A current proportional to a drive signal is supplied to the VCM to control the acceleration of the head support mechanism supporting the read/write head. This known control system has problems that the response to a step input of the desired value overshoots greatly. Thus in the event of a malfunction of a position measuring unit, the head support mechanism supporting the read/write head moves at an extraordinary speed that exceeds the limit of the predetermined range. This can cause the support mechanism to collide with a stopper and damage the disk drive.
The disk access control system disclosed in Japanese published application JPA 2001-250345, stops the seek operation and reduces the speed of the read/write head to zero when the speed information is malfunctioning. Also, the desired speed is obtained from calculating the difference between the signal that represents the desired track and the signal that represents the head position. This art uses a differentiator for converting the head-position signal into a speed signal. This leads to complicated circuitry to implement these functions.
The load-unload type head control system disclosed in Japanese published application JPA 2002-93080 moves the read/write head at a high speed in a high-speed control mode for a seek operation, and a low speed in a low-speed control mode in loading the read/write head. Since the head-position signal is not provided in the low-speed control mode, the counter electromotive voltage of the VCM is measured and used instead of the head-position signal. This art is a low-speed control, different from an art for positioning a read/write head at a desired track.
Accordingly, what is needed is a disk drive that is capable of positioning a head in a reliable manner.